1. Field of the Invention
This invention relates to conveyors for particulate material and more especially to relatively slow speed drag conveyors and aero mechanical conveyors.
2. Related Art
Slow speed drag conveyors and aero mechanical conveyors are of tubular construction and include a tensioned wire rope or chain to which are fitted a plurality of spaced plastics discs running between terminal sprockets. These conveyors operate at relatively slow speeds and effectively drag particulate material along the conveying tubes to a selected outlet valve. Throughputs of the order of between 8 and 32 m.sup.3 per hour are typical. The tubes of the conveyor may be aligned horizontally, vertically or may be inclined.
Products commonly handled by such conveyors include tea, sugar, detergents, flour, seeds, granules, gypsum, polymer powders and resins and the conveyors are used extensively in the food, pharmaceutical and chemical industries.
The presence of the wire rope discs or chain discs within the tubes places severe constraints on the position and operation of outlet valves. It is possible to use butterfly and slide valves as outlet valves; generally, however, they are unacceptable and have severe design disadvantages.
Rotatable valves have also been proposed in the past, but have been relatively expensive and susceptible to damage because of particulate material becoming trapped between abutting and stationary members of the valve and conveyor tubes. A rotatable valve for metering the flow of a stream of pneumatically conveyed dry particulate material such as cement is disclosed in U.S. Pat. No. 5,174,320.
U.S. Pat. No. 3,586,155 discloses a tubular conveyor assembly with spool-shaped conveyor flights. These are pulled through a tube by an endless cable driven by a sprocket wheel. Material leaves the assembly through a rotatable valve.
It is an object of this invention to provide an improved rotatable valve for tubular conveyors which does not suffer from or at least alleviates many disadvantages of existing valves.